The answer is to create separate DocumentDB clusters for user profiles and activity logs. This design decision is correct because mixed workloads with vastly different access patterns—such as the write-heavy, infrequently accessed activity logs versus the more balanced read-write profile data—compete for the same I/O and memory resources within a single cluster, leading to performance degradation and higher costs due to over-provisioning. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of workload isolation and cost optimization, often appearing as a trap where candidates mistakenly choose a single cluster with read replicas, which would not separate the write-heavy log traffic from the profile queries. A key memory tip is to think of “separate clusters for separate patterns”—logs are a write dump, profiles are a read-write service, so never mix them in one cluster.
DBS-C01 Workload-Specific Database Design Practice Question
This DBS-C01 practice question tests your understanding of workload-specific database design. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company is migrating a self-managed MongoDB database to Amazon DocumentDB. The database stores user profiles and activity logs. The activity logs are write-heavy and accessed infrequently. The company wants to optimize cost and performance for the workload. Which THREE design decisions should the company make?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable encryption at rest for both databases.
Option A is correct because enabling encryption at rest for Amazon DocumentDB is a security best practice that ensures data is encrypted using AWS Key Management Service (KMS) keys. This is a mandatory design consideration for compliance and data protection, and it does not significantly impact cost or performance for the workload described.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
Read the scenario before looking for a memorised answer.
✓
Use a t3.medium instance for the activity logs collection to reduce cost.
Why this is correct
A smaller instance is appropriate for infrequently accessed data.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use Amazon S3 for storing activity logs instead of DocumentDB.
Why it's wrong here
Activity logs are accessed infrequently but still require querying; S3 is not suitable for document queries.
✓
Create separate DocumentDB clusters for user profiles and activity logs.
Why this is correct
Separating workloads allows independent scaling and performance tuning.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a single DocumentDB cluster for both workloads with appropriate read replicas.
Why it's wrong here
Mixing different workloads can cause performance interference.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may assume a single cluster with read replicas is sufficient for mixed workloads, but the exam tests the understanding that separate clusters are needed to isolate write-heavy and read-heavy workloads for cost and performance optimization.
Detailed technical explanation
How to think about this question
DocumentDB uses a shared storage volume that automatically replicates data six times across three Availability Zones, and separate clusters for different workloads allow independent scaling of compute and storage. For write-heavy workloads, DocumentDB's storage auto-scales in 10 GB increments up to 64 TB, and using a smaller instance type like t3.medium may lead to CPU credit exhaustion and throttling under sustained write load. The correct approach is to use instance types from the r5 or r6g families for write-heavy workloads to ensure consistent performance.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Workload-Specific Database Design — This question tests Workload-Specific Database Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Enable encryption at rest for both databases. — Option A is correct because enabling encryption at rest for Amazon DocumentDB is a security best practice that ensures data is encrypted using AWS Key Management Service (KMS) keys. This is a mandatory design consideration for compliance and data protection, and it does not significantly impact cost or performance for the workload described.
What should I do if I get this DBS-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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